Airspray fuel injectors are commonly used in gas turbine engines. Such injectors use compressor discharge air to create a finely atomised fuel spray. The fuel nozzle of the injector typically has two or three air swirler circuits: an inner, an outer and a dome. An annular fuel passage between the inner and outer air circuits feeds air onto a prefilming lip. This forms a sheet of fuel that breaks down into ligaments, which are then broken up into droplets within shear layers of the surrounding highly swirling air.
FIG. 1 shows schematically conventional combustion equipment of a gas turbine engine. The annular combustion equipment 100 comprises outer 102 and inner 104 air casings, a flame tube 106, and a plurality of circumferentially distributed airspray fuel injectors 108.
Each fuel injector has a feed arm 110 which extends inwardly from an integral mounting flange 112 attached to the inner surface of a boss 114 formed in the outer casing. The feed arm ends in an injection nozzle 116 which penetrates a head of the flame tube 106. The nozzle includes a fuel passage(s) and air swirler circuits.
To provide an air seal at the point of entry of the injection nozzle 116 to the flame tube 106, the outer diameter of the nozzle is a close fit within a seal ring 118, known as a “miniflare”. Each miniflare is attached to the flame tube in such a way that it can move tangentially and radially relative to the combustion chamber, to allow for tolerances and differential thermal growths.
If the feed arm 110 were externally mounted to the outer casing 102, it would be necessary to admit the nozzle 116 through the casing. This would require a larger boss 114 to accommodate an aperture that could accept the passage of the nozzle, and hence would impose a weight penalty. Mounting the feed arm 110 internally to the outer casing 102 helps to avoid the weight penalty of a larger boss, but at the cost of more complex machining at the mounting flange-to-casing interface. Further, it precludes the replacement of a defective fuel injector without significant engine strip-down.